The Federal Rules of Civil Procedure
Pleadings and Motions
(a) When a Defending Party May Bring in a Third Party.
(1) Timing of the Summons and Complaint. A defending party may, as third-party plaintiff, serve a summons and complaint on a nonparty who is or may be liable to it for all or part of the claim against it. But the third-party plaintiff must, by motion, obtain the court's leave if it files the third-party complaint more than 14 days after serving its original answer.
(2) Third-Party Defendant's Claims and Defenses. The person served with the summons and third-party complaint—the “third-party defendant”:
(A) must assert any defense against the third-party plaintiff's claim under Rule 12;
(B) must assert any counterclaim against the third-party plaintiff under Rule 13a, and may assert any counterclaim against the third-party plaintiff under Rule 13(b) or any crossclaim against another third-party defendant under Rule 13(g);
(C) may assert against the plaintiff any defense that the third-party plaintiff has to the plaintiff's claim; and
(D) may also assert against the plaintiff any claim arising out of the transaction or occurrence that is the subject matter of the plaintiff's claim against the third-party plaintiff.
(3) Plaintiff's Claims Against a Third-Party Defendant. The plaintiff may assert against the third-party defendant any claim arising out of the transaction or occurrence that is the subject matter of the plaintiff's claim against the third-party plaintiff. The third-party defendant must then assert any defense under Rule 12 and any counterclaim under Rule 13(a), and may assert any counterclaim under Rule 13(b) or any crossclaim under Rule 13(g).
(4) Motion to Strike, Sever, or Try Separately. Any party may move to strike the third-party claim, to sever it, or to try it separately.
(5) Third-Party Defendant's Claim Against a Nonparty. A third-party defendant may proceed under this rule against a nonparty who is or may be liable to the third-party defendant for all or part of any claim against it.
(6) Third-Party Complaint In Rem. If it is within the admiralty or maritime jurisdiction, a third-party complaint may be in rem. In that event, a reference in this rule to the “summons” includes the warrant of arrest, and a reference to the defendant or third-party plaintiff includes, when appropriate, a person who asserts a right under Supplemental Rule C(6)(a)(i) in the property arrested.
(b) When a Plaintiff May Bring in a Third Party. When a claim is asserted against a plaintiff, the plaintiff may bring in a third party if this rule would allow a defendant to do so.
(c) Admiralty or Maritime Claim.
(1) Scope of Impleader. If a plaintiff asserts an admiralty or maritime claim under Rule 9(h), the defendant or a person who asserts a right under Supplemental Rule C(6)(a)(i) may, as a third-party plaintiff, bring in a third-party defendant who may be wholly or partly liable—either to the plaintiff or to the third-party plaintiff— for remedy over, contribution, or otherwise on account of the same transaction, occurrence, or series of transactions or occurrences.
(2) Defending Against a Demand for Judgment for the Plaintiff. The third-party plaintiff may demand judgment in the plaintiff's favor against the third-party defendant. In that event, the third-party defendant must defend under Rule 12 against the plaintiff's claim as well as the third-party plaintiff's claim; and the action proceeds as if the plaintiff had sued both the third-party defendant and the third-party plaintiff.